1. Field of the Invention
Ophthalmic lenses and more particularly lenses having controlled locally variable indices of refraction and/or high strength surface compression.
2. Discussion of the Prior Art
Lenses having locally variable indices of refraction are customarily fused multifocal lenses. These lenses show local variations of refractive index with discrete boundary surfaces between adjacent areas of different indices. As an example, a fused multifocal lens consisting of a major portion of refractive index 1.523 and at least one other segment portion having a higher refractive index fused onto a small portion of a surface of the major portion, the transition from the major to the higher index segment portion is conventionally produced by a fusion zone which causes a sharp, discontinuous change of the refractive index.
Ophthalmic lens designers have developed techniques for accomplishing multifocal effects and/or marginal corrections in lenses with aspheric surface design and wherewith the sharp discontinuous changes in refractive index can be avoided. The processes used, however, are difficult, cumbersome and costly mainly due to the need for producing the aspheric surfaces by mechanical means. Examples of aspheric lens surface designing may be found in U.S. Pat. Nos. 1,351,785; 2,869,422; 3,169,247; and 3,687,528.
Methods for producing locally variable refractive indices in glass bodies have also been developed with a view to overcoming the drawbacks of fused multifocals and/or problems encountered in the manufacture of aspheric surfaces. These methods, examples of which may be found in U.S. Pat. Nos. 3,873,408; 3,729,253; 3,486,808; and 3,212,401, utilize ion exchange processing to produce local alteration of refractive indices of the glass pieces. A major disadvantage of this processing is the low rate of production, i.e., taking several days of treatment to produce refractive index variations of significant thicknesses in lens materials. The limited number of ions available for utilization of ion exchange processing is still another disadvantage. An object of the present invention is to overcome the aforementioned and related drawbacks of prior art methods of accomplishing locally variable indices of refraction in ophthalmic lenses and to provide improved ophthalmic lenses together with greater ease, economy and dependability in their processing.
Other objects and advantages of the invention will become apparent from the following description.